Printed circuit board and method of manufacturing the same

ABSTRACT

There is provided a printed circuit board. The printed circuit board may be configured to include: a core layer in which a bending prevention portion of at least two layers is interposed between a plurality of insulating members and includes metal layers having different thermal expansion coefficients is disposed; a circuit pattern that is formed so as to have a desired pattern on at least one of the inside of the core layer and an outer face of the core layer; and an insulating layer that is formed on the core layer and includes an opening portion that exposes the circuit pattern, and a method of manufacturing the printed circuit board. According to the above-described printed circuit board and the method of manufacturing the printed circuit board, by disposing a bending prevention portion inside the printed circuit board, a printed circuit board capable of improving the progress rate and the productivity and a method of manufacturing the printed circuit board can be provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the priority of Korean Patent Application No.10-2009-0087152 filed on Sep. 15, 2009, in the Korean IntellectualProperty Office, the disclosure of which is incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed circuit board and a method ofmanufacturing thereof, and more particularly, to a printed circuit boardcapable of improving a manufacturing rate and productivity thereof bydisposing a bending prevention portion inside the printed circuit boardand a method of manufacturing the same.

2. Description of the Related Art

Recently, companies assembling and manufacturing circuit boards arefocused on super precision technology in accordance with the trend ofsemiconductor package boards towards lightness, thinness, andcompactness.

In particular, in a soldering process in which electrical bonding isconnected between a semiconductor package board and a main board, as thethickness of the board decreases, the importance of lessening thebending of the semiconductor package board increases.

The bending of the semiconductor package board markedly affects themanufacturing rate and productivity thereof in implementing such asoldering process.

In addition, the bending of the semiconductor package board may cause aproblem in which a solder ball is not formed on a solder ball pad of thesemiconductor package board in a soldering process, a problem in whichsolder balls formed on a semiconductor element and the semiconductorpackage board are not bonded to each other in the process of mountingthe semiconductor element, or the like, depending on the degree ofbending. Accordingly, the bending of the semiconductor package board isa very important factor that may cause a defective electrical connectionbetween the semiconductor element and the semiconductor package board.

A typical semiconductor package board is generally configured to have apackage area including a semiconductor element mounting portion, anouter-layer circuit pattern and a dummy area surrounding the packagearea.

In such a typical semiconductor package board, the thickness of theouter-layer circuit pattern of the package area or the thicknesses ofsolder resist layers of the package area and the dummy area arecontrolled in an effort to attempt to maintain the overall balance ofthe semiconductor package board so as to reduce bending.

Furthermore, as the thickness of the copper clad laminate used as theinner-layer board core decreases, the occurrence of the bending of thetypical semiconductor package board increases. Accordingly, there is aproblem, in that it becomes more difficult to reduce the bending of thesemiconductor package board by controlling the thickness of theouter-layer circuit pattern of the package area or the thicknesses ofthe solder resist layers of the package area and the dummy area.

SUMMARY OF THE INVENTION

An aspect of the present invention provides a printed circuit board anda method of manufacturing the same capable of improving themanufacturing rate and productivity thereof by disposing a bendingprevention portion inside the printed circuit board.

According to an aspect of the present invention, there is provided aprinted circuit board including: a core layer in which a bendingprevention portion of at least two layers that is interposed between aplurality of insulating members and includes metal layers havingdifferent thermal expansion coefficients is disposed; a circuit patternthat is formed so as to have a desired pattern on at least one of theinside of the core layer and an outer face of the core layer; and aninsulating layer that is formed on the core layer and includes anopening portion that exposes the circuit pattern.

The bending prevention portion may be configured to include a firstbending prevention layer having a first of thermal expansion coefficientand a second bending prevention layer having a second thermal expansioncoefficient that is higher than the first thermal expansion coefficient,from the opening portion side.

The bending prevention portion may be configured to include a secondbending prevention layer having a second thermal expansion coefficientand a first bending prevention layer having a first thermal expansioncoefficient that is lower than the second thermal expansion coefficient,from the opening portion side.

The first bending prevention layer may be formed from invar or nickel,and the second bending prevention layer is formed from copper or copperalloy.

The insulating layer may be a solder resist that is patterned so as toexpose the circuit pattern.

The core layer in which the bending prevention portion of at least twolayers that is interposed between the plurality of insulating membersand includes metal layers having different thermal expansioncoefficients is disposed may be included by replacing the insulatinglayer.

The printed circuit board may further include a solder resist that ispatterned so as to expose the circuit pattern on the core layer.

The printed circuit board may further include a through hole formed byperforating at least one face of the core layer.

According to another aspect of the present invention, there is provideda method of manufacturing a printed circuit board. The method includes:arranging a core layer in which a bending prevention portion of at leasttwo layers that includes metal layers having different thermal expansioncoefficients is disposed between a plurality of insulating members;forming a circuit pattern so as to have a desired pattern on at leastone of the inside of the core layer and an outer face of the core layer;and forming an insulating layer including an opening portion thatexposes the circuit pattern on the core layer.

The bending prevention portion may be formed of a first bendingprevention layer having a first thermal expansion coefficient and asecond bending prevention layer having a second thermal expansioncoefficient that is less than the first thermal expansion coefficient,from the insulating member side.

The bending prevention portion may be formed of a second bendingprevention layer having a second thermal expansion coefficient and afirst bending prevention layer having a first thermal expansioncoefficient that is higher than the second thermal expansioncoefficient, from the insulating member side.

The first bending prevention layer may be formed from copper or copperalloy, and the second bending prevention layer may be formed from invaror nickel.

The insulating layer may be formed as a solder resist that is patternedso as to expose the circuit pattern.

The forming of the core layer in which the bending prevention portion ofat least two layers that includes metal layers having different thermalexpansion coefficients between the plurality of insulating members isdisposed may be performed by replacing the forming of the insulatinglayer.

The forming of the core layer may further include forming a solderresist patterned on the core layer.

The forming of the core layer may further include forming a through holethat perforates at least one face of the core layer.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1A and 1B are schematic cross-sectional views illustrating aprinted circuit board including a bending prevention portion accordingto an exemplary embodiment of the present invention;

FIGS. 2A and 2B are schematic cross-sectional views of illustrating aprinted circuit board including a bending prevention portion accordingto another exemplary embodiment of the present invention; and

FIGS. 3A to 3F are schematic cross-sectional views illustrating aprocess for manufacturing a printed circuit board according to anexemplary embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Exemplary embodiments of the present invention will now be described indetail with reference to the accompanying drawings. The invention may,however, be embodied in many different forms and should not be construedas being limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. In the drawings, the shapes and dimensions may beexaggerated for clarity, and the same reference numerals will be usedthroughout to designate the same or like components.

Hereinafter, a printed circuit board having a bending prevention portionaccording an exemplary embodiment of the present invention will bedescribed in detail with reference to FIGS. 1 to 2.

FIGS. 1A and 1B are schematic cross-sectional views of a printed circuitboard including a bending prevention portion according to an exemplaryembodiment of the present invention. The printed circuit board accordingto the first embodiment will be described based on a two-layered printedcircuit board having a bending prevention portion as an example.

The printed circuit board 100A according to the exemplary embodiment ofthe present invention is configured to include a core layer 101 thatincludes a bending prevention portion 102 interposed between insulatingmembers 103 and 103′ and insulating layers 109 and 109′ that are formedon circuit patterns 104 and 104′, which are in turn formed on the innerside of the core layer 101 or the outer side of the insulating members103 and 103′, and the insulating members 103 and 103′ and includeopening portions O and O′ that expose the circuit patterns 104 and 104′so as to be bonded to solder balls.

Here, the bending prevention portion 102 is interposed between theinsulating members 103 and 103′. The bending prevention portion 102 isconfigured as two layers of metal having different thermal expansioncoefficients and is disposed in the core layer 101.

In a case where the printed circuit board 100A is used as an upper boardof a POP (Package On Package) board, the bending prevention portion 102is configured to include a first bending prevention layer 102 a having afirst thermal expansion coefficient and a second bending preventionlayer 102 b having a second thermal expansion coefficient which ishigher than the first thermal expansion coefficient, from the side of anopening portion O for bonding a solder ball in which a semiconductorelement is to be mounted later.

On the contrary, in a case where a printed circuit board 100B is used asa lower board of the POP board, the bending prevention portion 102 isconfigured to include the second bending prevention layer 102 b havingthe second thermal expansion coefficient and the first bendingprevention layer 102 a having the first thermal expansion coefficient,which is lower than the second thermal expansion coefficient, from theside of the opening portion O for bonding a solder ball in which asemiconductor element is to be mounted later.

As described above, a metal that can be configured as the bendingprevention portion 102 according to the first embodiment of the presentinvention, may be any arbitrary metal as long as the metal satisfies thecondition of configuring the first bending prevention layer 102 a havingthe first thermal expansion coefficient and the second bendingprevention layer 102 b having the second thermal expansion coefficientthat is higher than the first thermal expansion coefficient. As apreferred example, the bending prevention portion 102 according to thefirst embodiment of the invention may be configured to include invar ornickel (Ni) having a low thermal expansion coefficient as the firstbending prevention layer 102 a and copper or a copper alloy having athermal expansion coefficient higher than that of invar or nickel as thesecond bending prevention layer 102 b.

Commonly, as a printed circuit board for manufacturing a semiconductorpackage is exposed to a high-temperature heat through the manufacturingprocess, a phenomenon in which the printed circuit board is bent upward(the printed circuit board having a concave shape, when viewed from thelengthwise edge) or is bent downward (the printed circuit board having aconvex shape, when viewed from the lengthwise edge) occurs.

Described in greater detail, a printed circuit board mounted on theupper package board shows a tendency to be bent into a concave shape atroom temperature, and, on the other hand, to be bent into a concaveshape at a high temperature. In contrast to the behavior of the upperpackage board, a printed circuit board that is mounted on the lowerpackage board has a tendency to be bent into a convex shape at roomtemperature and to be bent into a concave shape at a high temperature.

In order to prevent the above-described printed circuit board bendingphenomenon which occurs during a semiconductor package manufacturingprocess or through a reflow process, by disposing a bending preventionportion that is configured by a metal having a low thermal expansioncoefficient and a metal having a high thermal expansion coefficient inthe printed circuit board that is mounted in the upper package boardwith the semiconductor mounting surface used as a reference, and bydisposing a bending prevention portion that is configured to have ametal having a high thermal expansion coefficient and a metal having alow thermal expansion coefficient in the printed circuit board that ismounted in the lower package board with the semiconductor mountingsurface used as a reference, stresses generated by the tendency to bebent that are generated in different directions are offset with eachother so as to perform a function of maintaining the printed circuitboard in a horizontal state, whereby the bending phenomenon of theprinted circuit board can be markedly decreased.

Here, the circuit patterns 104 and 104′ are formed on the inside ofthrough holes a and b, which are created by perforating one face and theother face of the core layer 101, or a part of the core layer 101 andboth outer sides of the insulating members 103 and 103′. In addition,the circuit patterns 104 and 104′ are formed so as to have predeterminedpatterns.

Here, the insulating layer 109 is formed on the insulating members 103and 103′ and includes the opening portions O and O′ that expose thecircuit patterns 104 and 104′ so as to be later bonded to solder balls.The insulating layer 109 may be configured by a patterned solder resist.

FIGS. 2A and 2B are schematic cross-sectional views of a printed circuitboard including a bending prevention portion according to anotherembodiment of the present invention. The printed circuit board accordingto this embodiment of the invention will be described based on afour-layered printed circuit board including a bending preventionportion as an example.

The printed circuit board 200A according to the second embodiment of thepresent invention is configured to include: a core layer 201 thatincludes a bending prevention portion 202 interposed between insulatingmembers 203 and 203′; core layers 205 that are formed on circuitpatterns 204 and 204′, in turn formed on the inner side of the corelayer 201 or the outer side of the insulating members 203 and 203′, andthe insulating members 203 and 203′; and a solder resist 209 that ispatterned so as to expose the circuit patterns 208 and 208′ of the corelayer 205.

Here, the bending prevention portion 202 is interposed between theinsulating members 203 and 203′. The bending prevention portion 202 isconfigured by two-layer metals having different thermal expansioncoefficients and is disposed in the core layer 201.

In a case where the printed circuit board 200A is used as an upper boardof a POP (Package On Package) board, the bending prevention portion 202is configured to include a first bending prevention layer 202 a having afirst thermal expansion coefficient and a second bending preventionlayer 202 b having a second thermal expansion coefficient, which ishigher than the first thermal expansion coefficient, from the side of anopening portion P for bonding a solder ball in which a semiconductorelement is to be mounted later.

In contrast, in a case where a printed circuit board 200B is used as alower board of the POP board, the bending prevention portion 202 isconfigured to include the second bending prevention layer 202 b havingthe second thermal expansion coefficient and the first bendingprevention layer 202 a having the first thermal expansion coefficient,which is lower than the second thermal expansion coefficient, from theside of the opening portion P for bonding a solder ball in which asemiconductor element is to be mounted later.

As described above, a metal that can be configured as the bendingprevention portion 202 according to the second embodiment of the presentinvention, may be any arbitrary metal, as long as the metal satisfiesthe condition of configuring the first bending prevention layer 202 ahaving the first thermal expansion coefficient and the second bendingprevention layer 202 b having the second thermal expansion coefficientthat is higher than the first thermal expansion coefficient. As apreferred example, the bending prevention portion 202 according to thesecond embodiment of the invention may be configured to include invar ornickel (Ni) having a low thermal expansion coefficient as the firstbending prevention layer 202 a and copper or copper alloy having ahigher thermal expansion coefficient greater than that of invar ornickel as the second bending prevention layer 202 b.

Here, the circuit patterns 204 and 204′ are formed on the inside ofthrough holes a′ and b′, which are created by perforating one face andthe other face of the core layer 201, or a part of the core layer 201and both outer sides of the insulating members 203 and 203′. Inaddition, the circuit patterns 204 and 204′ are formed so as to havepredetermined patterns.

Here, a core layer 205 is formed on the insulating members 203 and 203′.

Similarly to the core layer 201, a bending prevention portion 206 isalso disposed in the core layer 205.

In a case where the printed circuit board 200A is used as an upper boardof a POP (Package On Package) board, the bending prevention portion 206is configured to include a first bending prevention layer 206 a having afirst thermal expansion coefficient and a second bending preventionlayer 206 b having a second thermal expansion coefficient, which ishigher than the first thermal expansion coefficient, from the side of anopening portion P for bonding a solder ball in which a semiconductorelement is to be mounted later.

In contrast, in a case where a printed circuit board 200B is used as alower board of the POP board, the bending prevention portion 206 isconfigured to include the second bending prevention layer 206 b havingthe second thermal expansion coefficient and the first bendingprevention layer 206 a having the first thermal expansion coefficient,which is lower than the second thermal expansion coefficient, from sideof the opening portion P for bonding a solder ball in which asemiconductor element is to be mounted later.

Commonly, as a printed circuit board for manufacturing a semiconductorpackage is exposed to high-temperature heat through the manufacturingprocess, a phenomenon in which the printed circuit board is bent upward(the printed circuit board having a concave shape of a smile, whenviewed from the lengthwise edge) or is bent downward (the printedcircuit board having a convex shape, when viewed from lengthwise edge)occurs.

Described in greater detail, a printed circuit board mounted in theupper package board shows a tendency to be bent into a concave shape ata room temperature and to be bent into a convex shape at a hightemperature. In contrast to the behavior of the upper package board, aprinted circuit board that is mounted in the lower package board shows atendency to be bent into a convex shape at room temperature and to bebent into a concave shape at a high temperature.

In order to prevent the above-described bending phenomenon of theprinted circuit board that occurs during a semiconductor packagemanufacturing process or through a reflow process, by disposing abending prevention portion that is configured to have a metal having alow thermal expansion coefficient and a metal having a high thermalexpansion coefficient in the printed circuit board that is mounted inthe upper package board with the semiconductor mounting surface used asa reference and by disposing a bending prevention portion that isconfigured by a metal having a high thermal expansion coefficient and ametal having a low thermal expansion coefficient in the printed circuitboard that is mounted in the lower package board with the semiconductormounting surface used as a reference, stresses generated by the tendencyof being bent that are generated in different directions are offset witheach other so as to perform a function for maintaining the printedcircuit board in a horizontal state, whereby the bending phenomenon ofthe printed circuit board can markedly decreased.

Here, the circuit patterns 208 and 208′ are formed on the inside ofthrough holes a′ and b′, which are created by perforating one face andthe other face of the core layer 205, or a part of the core layer 101and outer sides of the insulating members 207 and 207′. In addition, thecircuit patterns 208 and 208′ are formed so as to have predeterminedpatterns.

Here, the insulating layer 209 is formed on the insulating members 207and 207′ and includes the opening portions P and P′ that expose thecircuit patterns 208 and 208′ so as to be later bonded to solder balls.The insulating layer 209 may be configured by a patterned solder resist.

Hereinafter, a process for forming the printed circuit board accordingto the first embodiment of the present invention will be described withreference to FIGS. 3A to 3F.

As illustrated in FIG. 3A, a core layer 101 is arranged by interposing abending prevention portion 102, which is formed by two-layers of metalhaving different thermal expansion coefficients, between insulatingmembers 103 and 103′. Here, the bending prevention portion 102 may beinterposed between the insulating members 103 and 103′ by beingthermo-compressed.

In a case of the core layer 101 having the printed circuit board 100A ofFIG. 1A is used as an upper board of a POP (Package On Package) board,the bending prevention portion 102 is configured to include a firstbending prevention layer 102 a having a first thermal expansioncoefficient and a second bending prevention layer 102 b having a secondthermal expansion coefficient, which is higher than the first thermalexpansion coefficient, from the side of an opening portion O, shown inFIG. 1A, for bonding a solder ball in which a semiconductor element isto be later mounted.

In contrast, in a case where the core layer 101, as the printed circuitboard 100B of FIG. 1B, is used as a lower board of the POP board, thebending prevention portion 102 is configured to include the secondbending prevention layer 102 b having the second thermal expansioncoefficient and the first bending prevention layer 102 a having thefirst thermal expansion coefficient, which is lower than the secondthermal expansion coefficient, from the side of the opening portion O,shown in FIG. 1B, for bonding a solder ball in which a semiconductorelement is to be later mounted.

As described above, as a metal that can be configured as the bendingprevention portion 102 according to the first embodiment of the presentinvention, any arbitrary metal can be used as long as the metalsatisfies the condition of configuring the first bending preventionlayer 102 a to have the first thermal expansion coefficient and thesecond bending prevention layer 102 b having the second thermalexpansion coefficient that is greater than the first thermal expansioncoefficient. As a preferred example, the bending prevention portion 102according to the first embodiment of the invention may be configured toinclude invar or nickel (Ni) having a low thermal expansion coefficientas the first bending prevention layer 102 a and copper or copper alloythat has a thermal expansion coefficient higher than that of invar ornickel as the second bending prevention layer 102 b.

Next, as illustrated in FIG. 3B, for interlayer circuit connections, athrough hole a and a blind via hole b are created in the insulatingmembers 103 and 103′. Then, an electroless copper coating layer 104 isformed in the through hole a and the blind via hole b.

Here, a method of forming the through hole a in a position set inadvance may be realized by using a CNC drill (Computer Numerical ControlDrill) is used. In addition, a deburring process in which dust generatedin a drilling process is removed from the side wall of the through holea and the surfaces of the insulating members 103 and 103′, and the like,may be performed further after the through hole a is created by usingthe CNC drill.

A method of forming the blind via hole b in a position set in advance byusing YAG laser (Yttrium Aluminum Garnet laser) or a carbon dioxidelaser (CO2 laser) may be used. In addition, a desmear process, in whichsmears generated due to melting from heat generated in the process forforming the blind via hole b on the side wall of the blind via hole b asthe insulating members 103 and 103′ and the bending prevention portion102 are melt, may be performed after the blind via hole b is formed byusing such laser.

As an embodiment, in the process of forming the electroless coppercoating layer 104, a catalytic deposition method that includes acleaning process, a soft etching process, a pre-catalyst process, acatalyst treatment process, an accelerator process, an electrolesscopper coating process, and an oxidation-prevention treatment processmay be used.

As another embodiment, in the process for forming an electroless coppercoating layer 104, a sputtering method in which the electroless coppercoating layer 104 is formed in the through hole a and the blind via holeb by colliding gaseous ion particles which are generated due to plasmaor the like (for example, Ar+) with a copper target.

As illustrated in FIG. 3C, after the electroless copper coating layer104 is coated with a dry film 105, a predetermined pattern is formed inthe dry film 105 by performing an exposure process and a developingprocess.

Here, the predetermined pattern includes a general outer layer circuitpattern, the area of the through hole a, the area of the via hole b, asemiconductor element mounting portion, a wire bonding pad pattern, asolder ball pad patter, and the like.

As an embodiment, in the process for forming the predetermined patternin the dry film 105, an artwork film (not shown) in which thepredetermined pattern is printed is brought into close contact with thedry film 105, and then an ultraviolet ray is emitted thereupon. As theultraviolet ray cannot be transmitted through a black portion in whichthe pattern of the artwork film is printed, the ultraviolet ray istransmitted through a non-printed portion whereby the dry film 105 underthe artwork film is cured. When the dry film 105 cured as describedabove is soaked in a developing solution, a portion of the uncured dryfilm 105 is eliminated by the developing solution. Accordingly, only aportion of the cured dry film 105 is left, whereby the predeterminedplating resist pattern is formed.

As illustrated in FIG. 3D, circuit patterns 104 a and 104 b formed byelectrolyte copper plating are formed in the areas of the electrolesscopper plating layer 104, the through hole a, and the blind via hole bby using the dry film 105 on which the predetermined pattern is formedas a plating resist. Next, the coated dry film 105 is peeled off so asto be removed.

Here, as a method of forming the circuit patterns 104 a and 104 b by theelectrolytic copper plating, after a raw material is eroded in a copperplating operation tank, electrolytic copper plating is performed byusing a DC rectifier. In the electrolytic copper plating, an area to beplated may be calculated, and an appropriate current is allowed to flowfrom the DC rectifier so as to deposit copper is used. The electrolyticcopper plating process has advantages in that the physicalcharacteristics of the copper plating layer are superior to theelectroless copper plating layer, and a thick copper playing layer canbe formed in an easy manner.

As in FIG. 3E, by performing a flash etching process in which an etchingsolution is sprayed, the electroless copper plating layer 104 located ina portion in which the circuit patterns 104 a and 104 b formed by theelectrolytic copper plating are not formed is removed.

In this process, the formation of the semiconductor element mountingportion 110 and the outer-layer circuit patterns 104 a and 104 b, andother dummy areas (not shown) of the package area according to anembodiment of the present invention is completed.

Next, as illustrated in FIG. 3F, an area positioned on the insulatingmembers 103 and 103′ on which the circuit pattern 104 a and theelectroless copper plating layer 104 are formed is coated with solderresists 109 and 109′ and is preliminarily dried. Then, by performing anexposure process, a developing process, and an etching process for theupper and lower solder resists 109 and 109′, the semiconductor elementmounting portion 110 in which a semiconductor element is mounted and anopening portion O, corresponding to a wire bonding pad that is connectedto the semiconductor element are formed in the upper solder resist 109,and an opening portion O′, corresponding to a solder ball pad that is tobe later connected to a motherboard and the like is formed in the lowersolder resist 109′. Next, the upper and lower solder resists 109 and109′ are completely cured.

Then, as illustrated in FIG. 1A, gold plating layers 111 and 111′ areformed in the semiconductor element mounting area 110, the wire bondingpad, and the solder ball pads that are the opening portions O and O′ ofthe upper and lower resists 109 and 109′.

In the embodiment, in order to improve the adhesiveness of the gold, thegold plating layers 111 and 111′ may be formed after nickel is thinlyplated thereupon.

According to an embodiment of the present invention, by disposing abending prevention portion inside the printed circuit board, a printedcircuit board capable of improving the progress rate and theproductivity and a method of manufacturing the printed circuit board canbe provided.

In addition, the printed circuit board that is manufactured according toan embodiment of the present invention can improve the assembly bydisposing the bending prevention portion inside the printed circuitboard. Accordingly, there is an advantage in that the manufacturingcosts can be reduced.

While the present invention has been shown and described in connectionwith the exemplary embodiments, it will be apparent to those skilled inthe art that modifications and variations can be made without departingfrom the spirit and scope of the invention as defined by the appendedclaims.

What is claimed is:
 1. A printed circuit board comprising: a core layerin which is disposed a bending prevention portion of at least two layersthat is interposed between a plurality of insulating members andcomprises metal layers having different thermal expansion coefficients;a circuit pattern formed so as to have a desired pattern on at least oneinner side of the core layer and an outer side of the core layer; and aninsulating layer formed on the core layer and including an openingportion that exposes the circuit pattern.
 2. The printed circuit boardof claim 1, wherein the bending prevention portion comprises a firstbending prevention layer having a first thermal expansion coefficientand a second bending prevention layer having a second thermal expansioncoefficient that is higher than the first thermal expansion coefficient,and the first bending prevention layer is formed such that the firstbending prevention layer is closer to the opening portion side than thesecond bending prevention layer.
 3. The printed circuit board of claim1, wherein the bending prevention portion comprises a second bendingprevention layer having a second thermal expansion coefficient and afirst bending prevention layer having a first thermal expansioncoefficient that is lower than the second thermal expansion coefficient,and the second bending prevention layer is formed where the secondbending prevention layer is closer to the opening portion side than thefirst bending prevention layer.
 4. The printed circuit board of claim 2,wherein the first bending prevention layer is formed from invar ornickel (Ni), and the second bending prevention layer is formed fromcopper or copper alloy.
 5. The printed circuit board of claim 3, whereinthe first bending prevention layer is formed from invar or nickel (Ni),and the second bending prevention layer is formed from copper or copperalloy.
 6. The printed circuit board of claim 1, wherein the insulatinglayer is a solder resist that is patterned so as to expose the circuitpattern.
 7. The printed circuit board of claim 1, further comprising athrough hole formed by perforating at least one face of the core layer.